In its 23rd year, the Bridger Mountains Raptor Migration Project continues to bring together birders, nature lovers and their concern for the animals’ habitat and wellbeing.
The project runs through Nov. 5. Peak eagle activity is in mid-October and, at that time, counts can reach as high as 200 eagles per day. A total of 17 species of raptors are observed during the count.
“The long-term data collected enables scientists to learn more about raptor migration patterns as well as regional and continental population trends,” Hawk Watch International Founder Steve Hoffman said. “The Bridger project is also designed to monitor widespread environmental changes using these raptors as barometers of ecological health.”
The ongoing effort, started by Hawk Watch International in 1991, monitors long-term trends in raptor populations using a helicopter platform atop Bridger Bowl Ski Area. In that area, two owl decoys are set high and in the clear to bring in the raptors. Fred Tilly discovered this spot in the northern portion of the Rocky Mountain Flyway more than 20 years ago. It takes about two hours to hike to the top.
“The flyway is noted for the largest concentration of Golden Eagles in the lower 48 states,” Hoffman said.
Two official counters make their home near the helicopter platform during the count’s 66 days. Bret Davis and Kalon Baughan are both returning for their second year of counting. At 8,600 feet, they have a 360-degree view in which to observe the migrating and resident raptors. They distinguish between the resident raptors and migrating birds by their behavior. If they move straight through north to south, they are likely migrating. If they defend their territory or dawdle a bit, they are likely residents.
The counters, who also record weather conditions each hour, capture about 95 percent of the migration timeframe and miss only about 20 percent of the raptors, according to Hoffman. They count the birds seven days a week from 10 a.m. to 6 p.m. They use these hours due to the wind patterns and the amount of possible sunlight. Each type of bird needs a different kind of lift to better and more easily make the migration. The counters use standard time – one hour back from daylight savings time – in their documentation since the birds do not change their clocks.
“We both love birds and the challenge of identifying hawks and eagles in flight,” Baughan said.
Satellite tracking of Golden Eagles born in Alaska and of migrants at locations in the western United States confirms that the Rocky Mountains encompass a primary migration corridor for Alaskan and Canadian eagles. The raptors travel as near as the Rocky Mountain front-range to the western Great Plains, and some go as far south as Mexico.
According to Hoffman, the number of Golden Eagles counted has declined by 40 percent in the past 15 years. The numbers are now holding steady, but not increasing. He said more study is needed to determine the cause of the decline, as well as its severity and extent. Factors affecting the Golden Eagle and other raptors’ populations include fires, logging, and beetle kill infested trees. The different species of raptors have different habitat needs as well.
The raptors are identified and recorded by age to the best of the counters’ abilities. They determine the bird’s species, age and gender from the animal’s tail, size and shape of the wings, wing beat, color and other factors.
“We wait until the bird goes by to be absolutely sure and we can see the head and tail,” Hoffman said.
A little more than halfway through the day’s count on Saturday, Baughan and Hoffman had counted 50 birds. Eleven of them were Golden Eagles. Hoffman estimated they would see maybe another 20 raptors while they were out there.
Coinciding with the count is the Bridger Raptor Fest. It happens the first weekend of October each year and is held at Bridger Bowl, annually. This year’s fest will be held Oct. 4-6.